Dosing apparatus has been described in U.S. Pat. No. 3,901,408 and is used for the volumetric dosing at a predetermined ratio of two components which are introduced as a reaction mixture into a mold through a mixing head.
One of the components may consist, for example, of polyhydroxyl compounds with a molecular weight of 62-10,000 and preferably 62-5000 containing two hydroxyl groups. Examples include polyesters, polyethers, polythioethers, polyacetals, polycarbonates and polyester amides containing at least two, generally 2 to 8, but preferably 2 hydroxyl groups. The other components may consist of aliphatic, cycloaliphatic, araliphatic and aromatic polyisocyanates. Readily available polyisocyanates are preferably used. These include tolylene-2,4-diisocyanate and any mixtures of this diisocyanate with its isomer as well as polyphenyl-polymethylene polyisocyanates.
The apparatus may also be used for so-called two-component resins, such as polyester resins and epoxide resins.
The apparatus is particularly suitable for dosing highly viscous components, even if they contain fillers. This requires high operating pressures, for example from about 20 bar to several thousand bar. At such high pressures, the use of a stretchable conduit system comprising pipes and flexible tubes affects the timing at which the components are injected into the mixing chamber of the mixing head. One of the reactants may therefore enter the mold cavity unmixed with the other component. Faults are thereby produced in the finished molded product.
It is an object of the present invention to provide an apparatus with which molded products can be produced which are free from faults of the type noted above. The apparatus can also be used for dosing highly viscous components at operating pressures which have not hitherto been attained.